I've read that the difference between the NP228 and NP229 is that the VC replaces the differential in a NP229. However, if that is true, then I agree with GWChris' argument as follows.

"Without a mechanical diff, you would have to drive one axle directly (like some of the cheap 4WD systems), and then the viscous coupling would send a little tourque to the other axle if there was a speed difference between them.

That's not how this works. It has an open diff with a viscous coupler in addition. If you drain out the secet fluid, then you just have an open diff left and it works like a NP228."

My NP 229 does not operate as if there is simply a VC in the front shaft. I do not have to have slippage in the rear wheels to get torque at the front.

Is the VC more complicated than just a set of parrellel plates in silicone fluid? Does it also have a mechanical differential function with the plates making it a limited-slip?

The NP228/229 transfer cases were Jeeps first transfer cases to receive the "Selec Trac" name, the later Selec Trac transfer case being the NP242. Both the NP228 and NP229 offer 2 wheel drive, Full Time 4 wheel drive in High range and Part Time 4 wheel drive in Low range. The NP228 uses an open differential for its front/rear power split in 4WD Fulltime High, the NP229 uses viscous coupling for its front/rear split in 4WD Fulltime High. Both lock the front/rear output shafts in 4 wheel drive in Low range. Both lack a 4 wheel drive Part Time High range mode.

However, I understand the basic function of the NP229 (how to shift, not to use low range on hard surfaces, etc). What I'm curious about is the exact function of the viscous coupling in the drive train. I believe it acts the same as a clutch pack in a limited-slip differential. But then there are some who swear the NP229 doesn't have a differential.

So I guess I'm looking for more gritty details from someone who has had one apart.

I searched on Google and this forum and just couldn't come up with the explanation I'm looking for.

Ristow Quote - "it's been a long while since i was into one that deep. but as my fuzzy memory serves,in the VC case,were spider gears engaged by stubs #2 and #6."

That explanation would make sense and fits with the way the 229 behaves in my opinion.

Chevelleguy,

I've never had one apart so I'm willing to believe you when you say the VC assembly doesn't have spider gears in it. But can you explain the flow of torque here? It looks to me like the VC is actually connected to the rear output. It is not possible that all of the power delivered to the rear wheels is transferred via the plates of the viscous coupling. Can you give any details as to the exact role the VC plays?

Here is what I know about VC's for industrial applications they are used to REPLACE a differential. The "fluid" is heavy enough, that if there is no torque difference there is not slip, so you have 50/50 split, but when you get a difference the VC allows for different speeds of the 2 shafts (slip).

A differential transfer torque, a VC allows different speeds between objects with a common driver, a limited slip in a differential tries to keep the torque close to 50/50 split even with unequal load on outputs, where an open differential will transfer 100% torque to the output with the least load.

Now, based on that a 229 can have the VC "burn out", and not turn the front drive shaft, you can then pin the VC and have 50/50 split like other part time cases.

Based on that the 229 DOES NOT have a true differential, it just uses a VC to allow for variance in drive shaft speed.

Here is what I know about VC's for industrial applications they are used to REPLACE a differential. The "fluid" is heavy enough, that if there is no torque difference there is not slip, so you have 50/50 split, but when you get a difference the VC allows for different speeds of the 2 shafts (slip).

A differential transfer torque, a VC allows different speeds between objects with a common driver, a limited slip in a differential tries to keep the torque close to 50/50 split even with unequal load on outputs, where an open differential will transfer 100% torque to the output with the least load.

Now, based on that a 229 can have the VC "burn out", and not turn the front drive shaft, you can then pin the VC and have 50/50 split like other part time cases.

Based on that the 229 DOES NOT have a true differential, it just uses a VC to allow for variance in drive shaft speed.

Sigh...I'm probably one of the 934+ people that are now confused beyond redemption. Let's try to get this answered for idiots like me with a simple question that hopefully addresses end results that matter to the driver.

With a 229 and no other mods:

1) When I'm running up or down a slippery road in 4WD High, whether its due to rain, mud, sand, snow, or ice, am I correct in that I can rely on at least one tire in the front and one tire in the rear will always have power to it? Yes/No?

I say "one tire" front or rear because we also have the front and rear differentials doing their thing too. And in this case we really have "2WD" because we're not locked. Yes/No?

2) But wait: If one has Limited Slip Differential in the rear (which I do), then I really have 3WD because both the rears will provide drive, but only one in the front will provide drive. Yes/No?

I don't remember seeing that part when I had mine apart. See how the side gears engage the clutch plates? It has to have the friction of the silicone fluid and the shear plates to transfer power. When all the fluid leaks out, you will have slippage or , if it is burnt real good, no forward movement in 4hi. That is why I tore into mine, it made a mechanical whine and had slippage, reduced forward motion, in 4hi.

I have had to go into one that wouldn't hold park and had no movement in 4hi. Replace with a good used coupling and it was fixed. Mine, I just pinned the coupling so now there is no differential action.